Electron gun structure with unipotential and bipotential lens

ABSTRACT

An electron gun structure having a main focusing lens including a unipotential electron lens and a bipotential electron lens, the unipotential and bipotential electron lenses serving as a single main electron lens having a larger effective aperture thereby greatly reducing aberration.

United States Paten 1191 Yamazaki et al. 1i Dec. 3, 1974 ELECTRON GUN STRUCTURE WITH 3,501,668 3/1970 -Pa ppadis 315/16 UNIPOTENTIAL AND BIPOTENTIAL LENS 3,651,359 3/1972 Mlyaoka 315/15 X [75] Inventors: Eiichi Yama'zaki, Ichihara; Hiromi K M b t f I I anal obara O h 0 apan Primary Examiner-Leland A. Sebastian Asslgneez Hitachi, y Japan Assistant ExaminerP. A. Nelson [22 Filed: Jan. 25 Attorney, Agent, or Firm-Craig & Antonelli [2]] App]. No.: 220,641

[30] Foreign Application Priority Data [57] ABSTRACT Feb. 5, 1971 Japan 46-4232 52 us. (:1 315/16 315/30 315/31 R An electron gun Structure having a main focusing lens 51 Int. Cl. .3 101 29/56 including a unipotemial electron and a biPotential [58] Field of Search 315/14-16 electm lens the unipmemial and bipotemial electron 315/30 31 R 31 lenses serving as a single main electron lens having a larger effective aperture thereby greatly reducing ab [56] References Cited erranon' UNITED STATES PATENTS 3,437,868 9 Claims, 5 Drawing Figures 4/1968 ,,Ohkoshi et al 315/15 ELECTRON GUN STRUCTURE WITH UNTPOTENTIAL AND BIPOTENTIAL LENS The present invention relates to electron gun structures, and more particularly to an electron gun structure having an electrode system capable of lens action for use in a cathode-ray tube.

As the electrode system capable of lens action for use in a cathoderay tube, there have heretofore been two types; the unipotential type and the bipotential type. In case of the unipotential type of electrode system, three focusing electrodes are used which are arranged on a common axis in order to form a main focusing lens assembly, two of the electrodes on both sides have applied thereto a common high voltage of, e.g., approximately 25kV, and the other electrode receives a voltage close to ground potential.

In contrast, in case of the bipotential type electrode system, two focusing electrodes are employed which are arranged on a common axis in order to form a main focusing lens assembly, one of the electrodes has applied thereto a high voltage of approximately 25kV, and the other receives a medium voltage of 3 to 6 kV.

These types of electrode system for an electron gun structure has the focusing electrodes arranged so as to constitute a single main electron lens, with the resultv that a cathode image is focused on the screen by the single main electron lens. In a cathode-ray tube, however, the aperture of the electron gun is restricted by the inside diameter of the neck portion in which the electron gun is received. The aperture of the main electron lens formed is accordingly subject to restriction, and the reduction of aberration is limited. This leads to serious problems especially in the three electron-gun type cathode-ray tube which accommodates three electron guns in the neck portion.

The present invention intends to solve such problems, and has its object in providing an electron gun structure which makes very small the aberration in the main electron lens without increasing the aperture of the electron gun, whereby an electron beam emanating from the electron gun is satisfactorily focused onto the screen.

According to the present invention, there is provided an electron gun structure having a plurality of electrodes for focusing an electron beam on a screen,- the improvement comprising a main focusing lens assembly comprising a first electrode means forming a unipotential electron lens anda second electrode means forming a bipotential electron lens.

In the accompanying drawings:

FIG. 1 is a diagram for explaining the basic construe tion of a main focusing lens system for use in an electron gun structure according to the present invention; and

FIGS. 2 to are schematic views of an electrode arrangement each showing an embodiment of the electron gun structure according to the present invention.

FIG. 1 shows the basic construction of the main focusing lens system used in the electron gun structure type electron lens L,, (or a bipotential type electron lens L,,) and the bipotential electron lens (or the unipotential electron lens). The electron lenses L, and L areadapted to form a main electron lens L,,,, which is larger in effective aperture. l, to I represent loci of electron beams.

When the main electron lens system L, is constructed of the two electron lenses L and L in this way, the effective aperture of the main electron lens may be made large, and hence, the aberration may be sharply decreased over the prior art. Since the two electron lenses L, and L consist, as described above, of the combination between the unipotential type electron lens L and the bipotential type electron lens L,,, the main electron lens system L, may reduce focal variations by means of the unipotential type electron lens L with respect to fluctuations in voltage, and it may also reduce an increased beam current by means of the unipotential type electron lens L with respect to blooming. Furthermore, owing to the use of the bipotential type electron lens L,,, a fine beam is easily obtained.

FIG. 2 illustrates an embodiment of the electron gun structure according to the present invention, and specifically shows only an electrode system forming the main electron lens system L,,, and. the way of supplying potentials thereto. Referring to the figure, the main electron lens system L,, is composed of an electrode system consisting of four electrodes, the first to fourth electrodes P to P arranged on a common axis, the first electrode P is arranged so as to be closest to the stem of the cathode-ray tube, and the fourth electrode P is arranged so as to be closest to the face panel of the cathode-ray tube. The electrode system has voltages supplied such that the first electrode P, and the third one P are connected in common to apply a high potential from a high potential source E to them, while the second electrode P and the fourth one P are connected in common to apply a medium potential from a medium potential source E to them, and thereby, a main focusing lens assembly is constructed. In the main focusing lens assembly thus constructed, the first to third electrodes P to P form the unipotential type electron lens L and the third and fourth electrodes P and P form the bipotential type electron lens L As has been explained with reference to FIG. ll, the lenses L and L form the apparently single main electron lens L,,,, of a larger effective aperture.

FIGS. 3 to 5 illustrate further embodiments of the electron gun structure according to the present invention, each specifically showing only the electrode system forming the main electron lens system L and the manner of supplying potentials thereto as in FIG. 2.

Referring first -to FIG. 3, among the four, first to fourth electrodes P, to P arranged on a common axis, the first and third electrodes P and P are in common connected to apply a high potential from a high potential source E, thereto, while the second and fourth electrodes P and P are respectively applied with different medium potentials from medium potential sources E and E Thus, the main focusing lens assembly is constructed. In the assembly, as in the foregoing case of FIG. 2, the first to third electrodes P to P form the unipotential type electron lens L while the third and fourth electrodes P and P form the bipotential type electron lens L In FIG. 4, among the four. first. to fourth electrodes P, to P arranged on a common axis, the first and third ones P, and P are connected in common to supply a medium potential from a medium potential source E thereto, while the second and fourth ones P and P are connected in common to supply a high potential from .a high potentialsource E,,'thereto. Thus, the main focusing lens assembly is constructed. In the assembly, opposite to the foregoing cases, the first and second electrodes P and P form the bipotential type electron lens L while the second to fourth ones P to P form the unipotential type electron lens L Further, according'to the embodiment of FIG. 5, among the four, first to fourth electrodes P, to P arranged on a common axis, the second and fourth ones P and P are connected in common to supply a high potential from a high potential source E thereto, while the first and third ones P and P are respectively supplied with different medium potentials from medium potential sources E and E Thus, the main focusing lens assembly is constructed. In the assembly, as in FIG. 4, the first and second electrodes P and P form the bipotential type electron lens L,,, while the second to fourth ones P to P form the unipotential type electron lens L As described above, the use of the electron gum structure according to the present invention provides a finebeam electron flow at small aberration, and accomplishes a very high resolution.

What we claim is:

1. In an electron gun structure having a plurality of electrodes for focusing an electron beam on a screen, the improvement comprising a main focusing lens assembly comprising first electrode means for forming a unipotential electronlens and second electrode means for forming a bipotential electron lens.

2. The electron gun structure as defined in claim 1, wherein said first electrode means includes first, second and third electrodes and said second electrode means includes said third electrode and a fourth electrode, said first, second, third and fourth electrodes being arranged on a common axis in order, said first and third electrodes being electrically connected to each other and supplied with a common high potential and each of said second and fourth electrodes being supplied with a potential lower than that of said first and third electrodes.

3. The electron gun structure as defined in claim 2, wherein said second and fourth electrodes are electrically connected to each other and are supplied with a common potential.

4. The electron gun-structure as defined in claim 2, wherein said second and fourth electrodes are supplied with individual potentials different from each other.

5. The electron gun structure as defined in claim 1, wherein said first electrode means includes second, third and fourth electrodes and said second electrode means includes a first electrode and said second electrode, said first, second, third and fourth electrodes being arranged on a common axis in order, said second and fourth electrodes being electrically connected to each other and supplied with a common high potential and each of said first and third electrodes being supplied with a potential lower than that of said second and fourth electrodes.

6. The electron gun structure as defined in claim 5, wherein said first and third electrodes are electrically connected to each other and are supplied with a common potential.

7. The electron gun structure as defined in claim 5, wherein said first and third electrodes are supplied with individual potentials different from each other.

8. The electron gun structure as defined in claim 2, wherein said third and fourth electrodes are of substantially equal diameter.

9. The electron gun structure as defined in claim 5, wherein said first and second electrodes are of substantially equal diameter. 

1. In an electron gun structure having a plurality of electrodes for focusing an electron beam on a screen, the improvement comprising a main focusing lens assembly comprising first electrode means for forming a unipotential electron lens and second electrode means for forming a bipotential electron lens.
 2. The electron gun structure as defined in claim 1, wherein said first electrode means includes first, second and third electrodes and said second electrode means includes said third electrode and a fourth electrode, said first, second, third and fourth electrodes being arranged on a common axis in order, said first and third electrodes being electrically connected to each other and supplied with a common high potential and each of said second and fourth electrodes being supplied with a potential lower than that of said first and third electrodes.
 3. The electron gun structure as defined in claim 2, wherein said second and fourth electrodes are electrically connected to each other and are supplied with a common potential.
 4. The electron gun structure as defined in claim 2, wherein said second and fourth electrodes are supplied with individual potentials different from each other.
 5. The electron gun structure as defined in claim 1, wherein said first electrode means includes second, third and fourth electrodes and said second electrode means includes a first electrode and said second electrode, said first, second, third and fourth electrodes being arranged on a common axis in order, said second and fourth electrodes being electrically connected to each other and supplied with a common high potential and each of said first and third electrodes being supplied with a potential lower than that of said second and fourth electrodes.
 6. The electron gun structure as defined in claim 5, wherein said first and third electrodes are electrically connected to each other and are supplied with a common potential.
 7. The electron gun structure as defined in claim 5, wherein said first and third electrodes are supplied with individual potentials different from each other.
 8. The electron gun structure as defined in claim 2, wherein said third and fourth electrodes are of substantially equal diameter.
 9. The electron gun structure as defined in claim 5, wherein said first and second electrodEs are of substantially equal diameter. 